Porous silicon or porous silicon oxide is used in microsystem technology in particular in the form of a thick layer having poor thermal conductivity, for the thermal decoupling of sensor structures or actuator structures in components such as thermal, chemical or fluid sensors or gas sensors. The quality of the thermal decoupling, and thus the quality of the component, depends to a large degree on the thermal conductivity of the material used for the decoupling. Minimal thermal conductivity measured on oxidized porous silicon having still tenable mechanical stability lie in the range of 0.3 to 0.5 W/mK.
To produce porous silicon or porous silicon oxide, one utilizes an electrochemical reaction between hydrofluoric acid and silicon. In the process, a silicon layer or a silicon wafer is polarized anodically with respect to a hydrofluoric-acid electrolyte, so that a sponge-type structure is produced in the silicon, which has a large inner surface and other chemical and physical properties, such as lower thermal conductivity, than the surrounding bulk silicon.